FILTRATION APPARATUS AND FAN ASSEMBLIES

摘要

A method of assessing the contamination state of a filter (17) particularly for air and forming a part of a filter assembly (10) including a wall (15) having an opening (16) with the filter (17) mounted thereover, at least one fan (18) being arranged to cause air flow through the filter. A passage (20) having a relatively small area compared to the area of the opening (16) is provided in association with the filter (17) so that air flows through the passage (20) on operation of the fan (18). The contamination state of the filter (17) is assessed from the detected speed of air flow through the passage.